Snow evaluators#

Evaluators used for solving snowpack and/or snow redistribution laterally.

SnowSurfacePotential#

Computes the potential surface upon which snow redistribution acts.

Snow distribution moves snow precipitation around to ensure that low-lying areas fill up first. This represents a potential field driving movement of snow precip, so defines what we mean by low-lying.

\[h + z + h_{{snow}} + dt * P_{{snow}}\]

“evaluator type” = “snow skin potential”

snow-skin-potential-evaluator-spec

  • “dt factor [s]” [double] A free-parameter factor for providing a time scale for diffusion of snow precipitation into low-lying areas. Typically on the order of 1e4-1e7. This timestep times the wave speed of snow provides an approximate length of how far snow precip can travel. Extremely tunable! [s]

KEYS:

  • “ponded depth” SURFACE_DOMAIN-ponded_depth [m]

  • “snow depth” DOMAIN-depth [m]

  • “precipitation snow” DOMAIN-precipitation [m s^-1]

  • “elevation” SURFACE_DOMAIN-elevation [m]

Example:

<ParameterList name="snow_skin_potential" type="ParameterList">
  <Parameter name="evaluator type" type="string" value="snow skin potential" />
  <Parameter name="dt factor [s]" type="double" value="864000.0" />
</ParameterList>

Snow Melt Rate#

Evaluates snow melt via USDA - Natural Resources Conservation Service model

From: National Engineering Handbook (NEH) part 630, Chapter 11

Snow melt rate is given by:

\[SM = H(T_{snow}^{expected} - 273.15) R\]

where \(R\) is the snow melt rate per degree-day and \(T_{snow}^{expected}\) is the expected snow temperature, which is typically given by \(T_{snow}^{expected} = T_{air} - \Delta\), where \(\Delta\) is the expected air-snow temperature difference [C] (note this is NOT prescribed here – the user must supply the expected snow temperature via an evalutor).

Note that the Heaviside function is used to ensure this is only active when the expected snow temperature is above 0 C.

Then, a linear transition factor is applied to ensure that this goes to zero as the snow SWE goes to zero. That factor is 1 at the snow transition depth, and 0 when snow SWE is 0. This uses LandCover for the snow_ground_transition parameter.

snow-meltrate-evaluator-spec

  • “snow melt rate [mm day^-1 C^-1]” [double] 2.74 the melt rate per degree-day, above 0 C, e.g. \(R\) above.

KEYS:

  • “snow water equivalent” DOMAIN-water_equivalent

  • “expected snow temperature” DOMAIN-expected_temperature